Circuit board with self-locking terminals

ABSTRACT

The present invention provides an apertured circuit board having self-locking terminals which partially cover at least some of the apertures. The terminals, which are integral extensions of the circuit pathways, each include a pair of inwardly disposed generally L-shaped fingers. The terminals are adhesively anchored to the circuit board at the terminal peripheries and are covered in part by a dielectric overlay. The latter also provides environmental protection and electrical insulation to the circuit conductive pathways. The circuit board and integral sockets may be formed by photoimaging and chemical milling techniques.

The present application is a continuation-in-part of my co-pendingapplication Ser. No. 808,808 filed June 22, 1977 now U.S. Pat. No.4,107,836.

This invention relates to electrical circuit assemblies and methods ofmanufacturing the same, and more particularly to improvements in circuitboards and to method for manufacturing the same.

In general, a printed circuit board comprises an electrically insulatingbase having an individual or composite electrical conductive pathways onat least one surface thereof, and one or more apertures communicatingbetween opposite surfaces on the insulating base. At least some of theapertures are surrounded at least in part by extensions of theconductive pathways ("terminals") which provide connection pointsbetween the conductive pathways and electrical and electroniccomponents. Numerous systems are well known in the art for mountingelectrical and electronic components and connectors onto printed circuitboards. Typically, the components are provided with leads, in which casethe components can be mounted to the board with their leads extendinginto and through the board apertures. Permanent electrical andmechanical connection between the components and the circuit board isachieved by soldering the components leads to the terminals surroundingthe apertures. The component leads may be individually soldered to theboard, e.g. as by hand soldering. However, connecting each lead in suchmanner is a tedious process. Accordingly, the art has developed varioussystems by which a plurality of soldered connections to a circuit boardmay be accomplished in a single mass soldering operation, e.g. employingpot soldering or wave soldering techniques.

Although soldered connections are considered to be highly effective toestablish reliable electrical and physical connections between componentleads and a circuit board, the soldering operation adds significantly tomanufacturing costs. Furthermore, it generally is necessary to cleansoldered assemblies following soldering, and such cleaning also may addappreciably to manufacturing costs. Moreover, the relatively hightemperatures typically required by mass soldering operations may damageheat sensitive components and/or may warp or delaminate the circuitboard. Still another disadvantage of soldering is that replacing afaulty component is relatively time consuming and difficult, requiringboth unsoldering and re-soldering operations. Moreover, such unsolderingand re-soldering operations may result in damage to the circuit board,adjacent components or other soldered connections on the board.

Solderless wrapping, crimping and socketing are known in the art andoffer alternative methods to soldering for mechanically and electricallyconnecting electrical and electronic components onto printed circuitboards. Such methods rely on metal deformation of the jumper wire, thecomponent lead or socket elements, or both, to form a metallurgicallysealed electrical interface. Typically such methods require specialequipment, are generally labor intensive, and also may have certainconnection spacing requirements which limits their application in thecase of high density configurations. Moreover, the stability ofinter-connections formed by such methods depends in part upon theresidual elastic stress remaining in the deformed metal, and thus mayfail in the field due to stress relaxation. An additional requirement ofsuch methods is to provide sufficient degree of metal deformation tobreak-down any surface oxides and other surface contaminations that maybe present on the mating metallic members, i.e. so as to assure a truemetal-to-metal contact. As a practical matter a common practice in theart is to plate the mating members prior to assembly with anon-corrosive metal such as gold. Such plating requirements may addsignificantly to manufacturing costs. Moreover, while such prior artsolderless interconnections theoretically offer an advantage oversoldered connections of easy separability, in practice solderlessinterconnections may be subject to degradation due to metal loss fromone or both contacting members upon repeated mating and unmatinginterconnections. Thus, such prior art solderless interconnectionspotentially offer advantages over soldered interconnections only incertain applications.

Still other methods of forming interconnections between printed circuitboards and electrical components are described in Swengel U.S. Pat. No.2,958,064 and Hotine et al U.S. Pat. No. 3,275,736.

Swengel proposes forming a laminated circuit board with integral socketsfor gripping electrical component leads or the like. According toSwengel, one or more layers or sheets of a resilient and rubbery-typematerial are bonded to a circuit board. The resilient sheets includeapertures corresponding in location to the circuit board apertures. Theapertures in the resilient sheets are of a diameter slightly less thanthat of the lead to be inserted therein, whereby the resilient sheetsmay mechanically grip a lead loaded in its apertures. In order to assureelectrical continuity a circuit extension, preferably integral with thecircuit pathways, is provided projecting into the aperture. An obviousdisadvantage of the Swengel circuit board is the need for resilientsheets which may add to the cost of manufacture and may alsosubstantially increase the weight of the board. Moreover, Swengel'sresilient sheets prevent visual inspection of the circuit, e.g. todetect defects. Still another disadvantage of Swengel is the reliance onthe mechanical force of deformation of rubbery-type materials to lockthe component and board together. As is well known in the art suchforces may lessen in time due to physical effects such as creep orstress relaxation and thus result in circuit failure in the field.

Hotine et al disclose an electrical connecting unit which basicallycomprises an apertured circuit board having a plurality of relativelythin finger-like spring members disposed so as to extend partly over theboard apertures. The finger-like members have pointed ends, and areconfigured so as to define an aperture with respect to one another whichaperture is slightly smaller in dimension than the cross-section of thecomponent leads to be inserted therein. According to Hotine et al thefinger-like members mechanically lock the component leads to the board;however, the required electrical connections to the circuit pathways aremade by spot welding the individual finger-like members to the leads.Hotine et al reports that such redundant multiple welds result inimproved reliability of the interconnections in the field. Obviously,the Hotine et al system is relatively costly. Moreover, the Hotine et alsystem is not believed to be practical in the case of high densityapplications due to the connection geometry, and the requirement forsufficient tie down area for adhesive or mechanical attachment of theindividual finger-like members to the board. Moreover, substantialconnector spacing is required to permit access to the individualfinger-like members for welding.

It is thus a principal object of the present invention to provide anovel interconnection system for electrically and mechanically attachingelectrical and electronic components to a printed circuit board. Anotherobject of the invention is to provide a solderless interconnectionsystem which overcomes the aforesaid problems of the prior art. Yetother objects of the present invention are to provide novel printedcircuit boards having integral solderless self-locking terminals formating with component leads, socket elements, jumper wires, and the likeand to methods for producing circuit boards of the type above described.

In my co-pending application Ser. No. 808,808 I disclose an aperturedcircuit board having self-locking terminals partially covering at leastsome of the apertures. According to my aforesaid application Ser. No.808,808, the terminals, which include spring member integral extensionsof the circuit pathways, are adhesively anchored to the circuit board atthe terminal peripheries and by a dielectric overlay. The latter is alsosaid to provide environmental protection and electrical insulation tothe circuit conductive pathways. A particular feature and advantage ofthe invention of my aforesaid application Ser. No. 808,808 is said toreside in an unique tie-down shoulder on each terminal which increasessubstantially the anchoring force provided by the dielectric overlay.Apertured circuit boards with self-locking terminals in accordance withmy aforesaid application Ser. No. 808,808 may be formed by photo-imagingand chemical milling techniques.

While apertured circuit boards having self-locking terminals made inaccordance with the teachings of my aforesaid application Ser. No.808,808 provide a substantial improvement over solderlessinterconnection systems such as wire wrapping, crimping and socketing,and in particular laminated circuit boards with integral sockets made inaccordance with the teachings of Swengel U.S. Pat. No. 2,958,064, supra,and the spring finger locking members of Hotine et al U.S. Pat. No.3,275,736, supra, manufacturing tolerances must be relatively closelycontrolled to predetermined dimensions. For example, if the terminal padspring members are too long, i.e. the spring members extend too faracross the board apertures, loading of component leads, etc., into theterminal pads may be somewhat difficult. Also, too long terminal padspring members may render difficult the removal of component leads. Onthe other hand, too short terminal pad spring members may produceinadequate electrical and mechanical connections. Manufacturingtolerances in accordance with the teachings of my aforesaid applicationSer. No. 808,808 also must be adhered to in order to prevent adhesiveflow onto the terminal pad spring members. Moreover, apertured circuitboards having self-locking terminals made in accordance with the priorart generally cannot mate with blade-type contacts, or with round leadsof diameter less than about 0.030 inches.

Generally, the present invention involves an apertured circuit boardhaving self-locking terminals which are integral extensions of thecircuit pathways. The terminals include a pair of dissimilar sizedL-shaped spring fingers. The L-shaped fingers are disposed, free endsfacing one another, to overlay an associated aperture. The free ends ofthe spring fingers are spaced from the circuit board, while the endsopposite the free ends are adhesively anchored to the circuit boardadjacent the terminal peripheries, and are tied-down by a dielectricoverlay. The latter also provides environmental protection andelectrical insulation to the circuit conductive pathways. A tie-downshoulder on each terminal increases substantially the anchoring forceprovided by the dielectric overlay. The circuit board and the integralsockets may be formed by photo-imaging and chemical milling (etching)techniques as will be described in detail following.

As used herein the term "printed circuit board" is intended to refer tocircuit boards formed by conventional photo-imaging and etchingtechniques as well as by stenciling and the like. The particular circuitdesign is a matter of choice and will be determined by desiredelectrical and electronic considerations well known to the art and whichform no part per se of the instant invention. The terms "electrical andelectronic components" are intended to refer to both active and passiveelectronic components, lead and jumper wires, socket elements and thelike.

For a further understanding of the nature and objects of the presentinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawings wherein like numbersdepict like parts and:

FIG. 1 is a top plan view of one form of circuit board constructed inaccordance with the present invention;

FIG. 2 is a side elevational view, partly in section of the circuitboard of FIG. 1, and showing an exemplary connection to an electricallead;

FIG. 3 is an enlarged top plan view, showing a single terminal andassociated aperture of the circuit board of FIG. 1;

FIG. 4 is a side elevational view, diagrammatically illustrating aprocess for producing the circuit board of FIG. 1;

FIGS. 5-14 are side elevational views of a circuit board at variousstages of formation in accordance with the process of FIG. 4;

FIG. 15 is a side elevational view, partly in section, showing analternative construction of circuit board made in accordance with theinstant invention; and

FIG. 16 is an enlarged top plan view, showing an alternate form ofterminal and associated apertured circuit board made in accordance withthe instant invention.

One embodiment of circuit board with self-locking terminals inaccordance with the present invention is shown in FIGS. 1-3 of thedrawings. In the embodiment of FIGS. 1-3 the circuit board comprises arigid dielectric panel or base sheet 20 of conventional circuit boardinsulating material, e.g. 0.062 inch thick phenolic resin board. (Forconvenience of illustration only a portion of the circuit board is shownin the drawings). A plurality of electrically conductive circuitpathways 22, each comprising an elongate central portion 24 extendingbetween terminal pad ends 26 and 28, respectively, are provided on atleast one surface, e.g. surface 30 of panel 20. For convenience ofillustration, circuit pathways 22 are illustrated as being provided ononly one surface 30 of panel 20. It will be understood however, thatcircuit pathways 22 may be provided on the panel 20 opposite surfaces.Alternatively, panel 20 may comprise a plurality of insulating panelsand may include one or more internally carried layers of circuitpathways. The conductive pathways have dimensions and shapescorresponding to desired design cirteria, e.g. current carrying capacityand circuit geometry. One or more aperatures 32 are formed through panel20 communicating between opposite surfaces on the panel.

As seen in the drawings terminal pads 26 and 28 are integral extensionsof central portions 24. Pads 26 and 28 are larger in plan than apertures32, and the pads partially cover the apertures 32 at least in part.Apertures 32 typically are round holes. As will become clear from thedescription following the diameter of apertures 32 will depend in parton the diameter of the lead to be loaded therein. For example, for atypical lead of about 0.030 inch diameter aperture 32 should have adiameter of about 0.010 to 0.030 inches. Referring particularly to FIGS.1 to 3 each terminal pad (e.g. pad 26) includes a generally circularframe member 34 and inwardly disposed spring fingers 36 and 38. As seenin FIG. 3 spring fingers 36 and 38 each constitute an L-shaped memberand are formed (deflected) upwardly from panel 30 (see FIG. 2). One ofthe spring fingers (e.g. finger 36) is somewhat longer than the otherfinger 38, however, the longer finger 36 is deflected further upwardlythan the shorter finger 38 so that the far edges 37 and 39 of fingers 36and 38, respectively, essentially lie on a line which dissects aperture32. Spring fingers 36 and 38 are formed integrally with frame member 34;the latter in turn is formed integrally with an associated circuitpathway 22. An important feature and requirement of the presentinvention is to make the two spring fingers of different size, i.e. onespring finger 36 should be longer than the other spring finger 38 sothat in undeflected state (see FIG. 13) the longer finger 36 would thusextend further across aperture 32. Also, spring fingers 36 and 38 shouldbe shaped and dimensioned so that when undeflected the facing edges ofthe spring fingers define a generally rectangular interspace ofapproximately 0.030 inches by 0.020 inches. Forming spring fingers 36and 38 of different size as shown in FIG. 13, and deflecting the fingersupwardly from panel 20 as shown in FIG. 2 facilitates loading andunloading component leads, etc. in the board as will become clear fromthe description following.

As mentioned above terminal pads 26 should be substantially larger inoverall plan than apertures 32, and the pads should be "centered" overthe apertures. Another feature and requirement of the present inventionis to space spring fingers 36 and 38 from the surface 30 of panel 20.This latter feature and requirement is achieved by making the springfingers 36 and 38 thinner in cross-section than frame member 34 by amanufacturing process as will be described in detail hereinafter. By wayof example but not limitation, assuming frame member 34 has a thicknessof about 0.010 inch, spring fingers 36 and 38 may be spaced about 0.001to 0.009 inches from surface 30 and may have a thickness of about 0.009to 0.001 inches. Making the spring fingers 36 and 38 thinner than theirsupporting frame member 34, and spacing the spring fingers from theboard surface 30 increases flexibility of the fingers, and reduces thepossibility of adhesive flow onto the spring fingers during manufactureas will be described in detail hereinafter.

As in the case of the circuit board described in my aforesaidapplication Ser. No. 808,808 terminal pads 26 and 28 are called upon toperform the four-fold functions of (1) electrically connecting theconductor central pathways 24 and the component leads or wires, (2)mechanically hold and maintain the wires or components leads, to theboard, (3) permit assembly of wires or leads by simple mechanicaldeflection, and (4) apply relatively high pressure against the wires orleads throughout the design life of the assembly.

A deficiency of prior art self-locking terminal boards, e.g. as taughtby Swengel is the failure to provide sufficient mating or hold-down areabetween the circuit terminals and the substrate board for adequatelyadhesively anchoring the terminals to the board. Sufficient hold-downarea is required to prevent the terminals for delaminating from theboard during lead insertion or removal and also to ensure a constantoperating force. As will be appreciated providing sufficient hold-downarea between the terminals and the surrounding board may present aparticularly acute problem in the case of high density applications. Inmy aforesaid copending application Ser. No. 808,808 I describe asolution to the problem of terminal pad hold-down by providing theterminal pads with outwardly depending integral shoulders or steps ofreduced thickness relative to the main body of the terminal. Theshoulders can then be captured under a dielectric overlay, and therebyanchored to the board. The present invention incorporates a similarsolution to the hold-down problem by providing outwardly dependingintegral shoulders or steps 42 of reduced thickness on the peripheriesof the terminal pads 26 and 28. For example, assuming a terminal pad ofthickness of about 0.010 inches measured at main frame member 34,shoulders 42 may have a thickness in the range of about 0.001 to 0.005inches, preferably about 0.003 inches. Providing outwardly dependingshoulders on the terminal pads provides a capture area for adhesivecoated dielectric overlay 44. Thus, as seen in FIG. 2 the terminal ends,e.g. the flat bottom surface of terminal pad 26 and its associatedconductor pathway 24 are bonded to the top surface 30 of rigid panel 20by an adhesive 46. Overlay 44 is also bonded to the top surface of panel20, and the top surface of the conductor pathways 22. Overlay 44 alsoextends over terminal shoulders 42 whereby to capture and cover theshoulders 42 at least in part. As seen in FIGS. 1 and 2 overlay 44preferably extends to the main, e.g. full thickness areas of terminalpad frame members 34. Overlay 44 may be formed of an electricallyinsulating polymeric film material such as a polyester, polypropylene,polyimide, cellulose triacetate, polyethylene terephthalate or othercommercially available film, e.g. as in accordance with my aforesaidcopending application Ser. No. 808,808; preferably however, overlay 44compises a rigid dielectric sheet or board such as phenolic board whichmay be the same or different thickness as the base sheet 20. Overlay 44bonded to the circuit rigid panel 20, terminal pads 26 and 38, shoulderareas 42 and the conductor pathways 22 by suitable adhesive means suchas a modified epoxy, or acrylic based adhesive.

FIGS. 4-14 illustrate one method of forming a circuit board havingintegral self-locking terminals in accordance with the presentinvention.

An electrically conductive, resiliently flexible metallic sheet 50preferably of a thickness substantially equal to that desired for thefull thickness areas of terminal pads 26 and 28, i.e. frame members 34is provided. In the illustrated case metallic sheet 50 comprises 0.010inch thick phosphor bronze ST. One skilled in the art will recongizehowever that other electrically conductive, resiliently flexiblemetallic materials may be employed. The top and bottom surfaces 52 and54 of the metallic sheet 50 are then cleaned employing conventionaltechniques, and cleansed surfaces are then coated at a coating station56 (FIG. 4) with conventional acid resist materials layers 58 and 60,respectively. Then one side of metallic sheet 50 (e.g. top side 52 andresist layer 58) is exposed to light, at an imaging station 62 to anegative art work image of the terminal pads frame members 34 and springfingers 36 and 38. Simultaneously bottom resist layer 60 is exposed tolight, at imaging station 62, to a positive art work image of theterminal area bounded by frame members 34. Those areas of resistcoatings 58 and 60 exposed to light are altered to a lower molecularweight polymer. The sheet is then immersed in a preferential solvent anddeveloped at a treating station 64, with the result that the exposedportions of resist layers 58 and 60 remain intact while the unexposedareas are dissolved leaving resist layer 58 in a positive image ofterminal pads 26 and 28, frame members 34 and spring fingers 36 and 38,and leaving resist layer 60 in a negative image of the area bounded byframe members 34.

The next step involves chemically milling the exposed metallic areas ofmetallic sheet 50 by contacting the sheet 50 with an acid etchingsolution at an etching station 68. Etching is controlled to remove metalfrom the unprotected terminal pad underside areas to a depth to leavemetal of thickness which substantially equals that desired for thespring fingers 34 and 36. For example, if 0.003 inch thick springfingers are desired, etching should be controlled to a depth of about0.007 inches. Obviously, the other unprotected areas of sheet 50 willalso be etched to a similar depth in the etching station 68 with theresult that the sheet 50 will also be thinned to partly define theterminal pad shoulders 42 as shown in FIG. 6.

Thereafter, the etched sheet is treated in a stripping station 70wherein the acid resist remaining on the sheet is removed from bothsides of the sheet. A metallic sheet having a contoured surface 72 withraised areas 74 and back-etched spring fingers 36 and 38 as shown inFIG. 7 results.

The next step in the process of the present invention is to partiallycover all but the terminal pad areas of the FIG. 7 sheet 50 with adielectric overlay in the form of a rigid electrically insulatingstiffening board such as 0.062 inch thick phenolic resin board 44. Board44 should be pre-drilled so as to cover substantially the entire surface52 of metallic sheet 50 other than the terminal pad areas. Board 44 isapplied to sheet 50 at a mounting and laminating station 78 (FIG. 4),and the board is laminated to the metallic sheet by means of a suitableadhesive, for example a B-stage thermoplastic adhesive such as one ofthe many modified acrylic adhesives as are commerically available. Aswill become clear from the description following dielectric overlay 44performs the two-fold functions of (1) mechanically anchoring theterminals to the substrate panel and (2) electrically insulating thecircuit pathways. A phenolic board/contoured metallic sheet laminate asshown in FIG. 8 results.

The FIG. 8 phenolic board/metallic sheet laminate is then returned tocoating station 56 where the uncovered surface 54 of sheet 50 is coatedwith layer 80 of a conventional resist material. Then using one or moreof the raised areas 74 to insure front-to-back image registration,resist layer 80 is exposed to a negative art work pattern whichessentially defines the areas subtended by apertured frame members 34 atimaging station 62. The sheet is then treated in treating station 62with the result that exposed areas of the resist layer 80 remain intactwhile the unexposed areas are dissolved away as before. The resultingstructure appears substantially as shown in FIG. 9. It should be notedthat at this stage in the process metallic sheet 50, while contoured andapertured, still is continuous.

The next step involves plating the exposed metallic areas of sheet 50 bya conventional plating technique, e.g. by electrodeposition, in knownmanner, of a precious or semi-precious material such as gold plate 81 ata plating station 82. Inasmuch as the metallic sheet 50 is stillcontinuous at this stage of the processing, assuring electricalcontinuity for plating purposes to each terminal end is assured. Overlayboard 44 effectively masks the entire top surface 52 of sheet 50 otherthan the terminal pad areas, while resist layer 80 effectively masks theentire bottom surface 54 of sheet 50 except areas subtended by theterminal pad frame members 34. As a result deposition of the preciousmetal is restricted essentially to those areas of sheet 50 whichultimately will become parts of the terminal pads and the springfingers. One skilled in the art will recognize an advantage of thepresent invention in that plating the terminals thus is an especiallysimple procedure, and which may result in a relatively low consumptionof precious metal. Still another advantage of the invention is that theactual contact edges of the spring fingers 34 and 36 are also plated.

Following plating the resist layer 80 is then stripped from surface 54at stripping station 70. The resulting structure appears substantiallyas shown in FIG. 10. Thereafter, using the plated areas as a resist, themetallic structure is returned to etching station 68 to complete thedefinition of the terminal pad frame members 34 and to define theconductors 22.

At this point, the resulting metal/phenolic board structure is passed toa forming station 90 where the spring fingers 36 and 38 are permanentlydeflected upwardly, i.e. away from the bottom surface 54 of sheet 50into their respective apertures in overlay board 44. As seen in FIG. 11forming station 90 includes a die block 92 having a plurality of formingpins 94 which are suitably sized and positioned to mate with theapertures in the overlay board 44. Deflection occurs in two steps withthe forming pins 94 initially contacting and deflecting at least in partthe shorter spring fingers 38 (see FIG. 13). Then the longer springfingers 36 are contacted by the forming pins 94, and deflected upwardlypast the at least partially deflected shorter spring fingers 36. Theresulting structure appears as shown in FIG. 14.

The final step involves mounting the FIG. 14 structure at mounting andlaminating station 78 onto a rigid panel or sheet 20 such as a 0.062 milphenolic resin board. The latter is predrilled with a plurality ofapertures 32. As seen in FIGS. 2 and 15 apertures 32 are located inpanel 20 to be concentric with circular frame members 34 when the panel20 is mounted onto the FIG. 14 structure. The metal/film structure isthen laminated to the rigid panel 20 in known manner, e.g. employing athermosetting adhesive, heat and pressure. An advantage of the presentinvention which becomes particularly evident at this step is that as aresult of the earlier etch processing the spring fingers are deflectedand raised above the surface of panel 20. Thus, the likelihood ofadhesive flow under the spring members 36 and 38 during lamination tothe rigid panel 20 is relatively remote. The resulting structure is aprinted circuit board of the type shown in FIGS. 1-3.

One skilled in the art will recognize that the mechanical locking forceof the terminal pad spring fingers 36 and 38 can be varied to meetspecific design requirements, for example by employing a metallicsubstrate material of desired spring characteristics and thickness, byadjusting the size and/or shape of the spring fingers 36 and 38, or by acombination of one or more of the foregoing. For example, if arelatively large spring force is desired, the metallic substratestarting material (sheet 50) may be spring steel. In such case it may bedesired to plate-up the terminal contact areas (station 82) with apreferred electrically conductive material such as copper, or copperplate followed by tin plate. Processing is otherwise as before. Anadvantage of the present invention which results from making springfingers 36 and 38 of different relative size and of pre-forming thefingers is seen in FIG. 2, in which there is shown a component lead 84loaded in a terminal pad made in accordance with the invention. Itshould be evident to one skilled in the art that because the springfingers 36 and 38 are L-shaped of different length relatively widevariations in finger dimensions can be toleranced. Moreover, since thespring fingers are pre-formed, component or wire lead insertion and/orremoval is also facilitated.

Various changes may be made in the foregoing process and product withoutdeparting from the spirit and scope of the foregoing invention. Forexample, the process can be modified to provide a circuit board havingflexible conductor pattern area 86, e.g. by providing rigid panels 20A,20B adjacent and supporting only terminal pads 26 and 28 (FIG. 15), asin accordance with the teachings of my aforesaid copending applicationSer. No. 808,808. Obviously, this will leave portions of the conductors32 exposed. In such case conductors 32 can be covered, if desired, bythin, flexible dielectric overlay films 88A and 88B which may beadhesively secured to conductors 22, rigid panels 30A, 30B and theterminal pads. The foregoing process of the present invention may alsobe adopted to produce two-sided or multi-layer circuit boards. Moreover,the terminal pads may be formed in the shape of a square or rectangle asshown in FIG. 16 rather than as round pads as shown in FIG. 3. Stillother changes will be obvious to one skilled in the art.

What is claimed is:
 1. A method of making a circuit board having (i) atleast one electrically conductive circuit pattern formed on a surface ofsaid board, and (ii) at least one shaped aperture formed between saidsurface and the surface opposite thereto, said method comprising thesteps of:(A) providing a resiliently flexible metallic panel; (B)removing material from selected areas on one surface of said metallicpanel while leaving (i) a substantially continuous metallic panel having(ii) at least one raised area, (iii) at least one area of reducedcross-section bounded by said at least one raised area, and (iv) atleast one shaped aperture in said at least one area of reducedcross-section; (C) removing material from the opposite surface of saidmetallic panel from selected areas opposite said at least one raisedarea; (D) providing a first, dielectric panel having at least oneaperture of approximate shape and location as said at least one raisedarea, and aligning and securing said first dielectric panel to saidmetallic panel so as to cover said one surface of said metallic panel atleast in part while leaving substantially uncovered said at least oneraised area; (E) masking selected areas on the other surface of saidmetallic panel so as to leave uncovered (i) areas opposite said at leastone raised area and including (ii) boarder areas surrounding said raisedareas; (F) plating the uncovered areas on both surfaces of said metallicpanel and removing said mask; (G) chemically milling said metallic panelemploying the resulting plated areas as resist whereby metallic materialis removed from said metallic panel leaving behind one or moreconductive circuit patterns and at least one shaped aperture; (H)providing a second, rigid dielectric panel having at least one aperturewhich is smaller than said at least one aperture in said metallic panel;(I) positioning said metallic panel and said second dielectric panel sothat said second dielectric panel is adjacent said other surface of saidmetallic panel and said at least one aperture in said metallic panel andsaid at least one aperture in said second, relatively rigid dielectricpanel are substantially aligned with one another; and (J) securing saidsecond dielectric panel and said metallic panel to one another.
 2. Amethod according to claim 1 wherein material is removed from selectedareas on said one and said opposite surfaces of said metallic panel bychemically milling said metallic panel.
 3. A method according to claim2, wherein material is removed from said one and said opposite surfacesin a single chemical milling step.
 4. A method according to claim 2 andcomprising the step of masking selected areas on said one surface ofsaid metallic panel with a resist material which is resistant to saidchemical milling.
 5. A method according to claim 1 wherein said metallicpanel comprises a phosphor bronze panel.
 6. A method according to claim1 wherein said first and said second dielectric panels each compriserigid panels.
 7. Method according to claim 1 including the step offorming said at least one aperture with a pair of inwardly disposeddissimilar size L-shaped fingers.
 8. Method according to claim 7including the step of deforming the free ends of said fingers away fromsaid metallic panel other surface.
 9. A method of making a circuit boardhaving (i) at least one electrically conductive circuit pattern formedon a surface of said board, and (ii) at least one shaped aperture formedbetween said surface and the surface opposite thereto, said methodcomprising the steps of:(A) providing a resiliently flexible metallicpanel; (B) removing material from selected areas on one surface of saidmetallic panel while leaving (i) a substantially continuous metallicpanel having (ii) at least one raised area (iii) at least one area ofreduced cross-section bounded by said at least one raised area, and (iv)at least one shaped aperture in said at least one area of reducedcross-section; (C) providing a first, rigid dielectric panel having atleast one aperture of approximate shape and location as said at leastone raised area, and aligning and bonding said first dielectric panel tosaid metallic panel so as to cover said one surface of said metallicpanel at least in part while leaving substantially uncovered said atleast one raised area; (D) masking selected areas on the other surfaceof said metallic panel so as to leave uncovered (i) areas opposite saidat least one area, and including (ii) boarder areas surrounding saidraised areas; (E) plating the uncovered areas on both surfaces of saidmetallic panel and removing said mask; (F) chemically milling saidmetallic panel employing the resulting plated areas as resist wherebymetallic materail is removed from said metallic panel leaving behind oneor more conductive circuit patterns and at least one shaped aperturecomprising a pair of spaced, inwardly disposed dissimilar size L-shapedfingers; (H) providing a second, relatively rigid dielectric panelhaving at least one aperture which is smaller than said at least oneaperture in said metallic sheet; (I) positioning said metallic panel andsaid second dielectric panel so that said dielectric panel is adjacentsaid other surface of said metallic panel and said at least one aperturein said metallic panel and said at least one aperture in said relativelyrigid dielectric panel are substantially aligned with one another; and(J) bonding said dielectric panel and said metallic panel to oneanother.